Tourists gathered in Las Vegas on Sunday to ring in the new year under the close eye of police just three months after the deadliest mass shooting in modern US history rattled the city.

Tourism officials expected New Year's Eve to see about 330,000 people on the Las Vegas Strip and downtown's Fremont Street.

The Las Vegas Metropolitan Police Department had every officer working on Sunday and was aided by the Nevada National Guard and federal agents.

"One bad incident is not going to deter us from having a good time," Honolulu resident Pettra Stark, who planned her trip after the October 1 shooting, said while standing underneath the massive video canopy on Fremont Street.

For Ms Stark, the heavy presence of armed officers was reassuring. But not everyone felt the same way, including Adrian Dominguez, who travelled for the festivities with 10 other relatives.

"It's not pleasant to see so many officers," Mr Dominguez, a resident of the northern Mexico border city of Ciudad Juarez. "They are everywhere."

The heightened security comes after a high-stakes gambler killed 58 and injured hundreds more after he shattered the windows of his suite on the 32nd floor of the Mandalay Bay hotel-casino on the Strip and unleashed gunfire on a country music festival below. He then killed himself.

On Saturday, two security guards were fatally shot while investigating a disturbance at Arizona Charlie's Decatur, a hotel-casino just west of the Strip.

The suspect was taken to hospital with a self-inflicted gunshot wound, police said. Authorities described it as an isolated incident and assured that it was not terrorism-related.

New Year's Eve festivities at this gambling oasis are anchored by a roughly eight-minute fireworks display at the top of seven casino-hotels.

Some of the biggest names in music including Bruno Mars and Britney Spears had shows scheduled on venues on the Strip, while several bands performed throughout the night on Fremont Street.